Transport Layer

• use
  • main responsibility, transfer the data completely
  • receives the data from the upper layer and converts them into smaller units known as segments.
  • termed as an end-to-end layer,provides a point-to-point connection between source and destination to deliver data reliably.
  • ensures that messages are transmitted in the order in which they are sent and there is no duplication of data.
  • end to end delivery of the data
  • udp and tcp protocols are used
  • flow control - don't send more data
  • congestion control - too many packets in the network
  • segmentation - dividing into packets
  • error correction
• protocols
  • TCP
  • UDP
• pdu
  • segment

Ports

• both udp and tcp have - (1-65535) number of ports, \(2^{16} - 1 = 65535\)
• because port no is a 18 bit number (2 byte)

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• well known ports - 1 to 23
• registered ports - 1024 - 49151, assigned by IANA, internet assigned number authority
• dynamic ports, generated by pc, bound by the port you create on pc, rest of remaining ports
• use netstat on windows

Some common ports

tcp

• ftp - 21, file transfer protocol
• ssh - 22
• telnet - 23
• smtp - 25
• http - 80
• https - 443
• pop - 110
• dns - 53

udp

• tftp - 69, trivial ftp
• dhcp - 67/68
• smtp
• dns - 53